Post-Election Procedures and Audits (In NC)
https://www.ncsbe.gov/about-elections/election-security/post-election-procedures-and-audits#reports
Heres how it works:
The day after each election, the State Board of Elections randomly selects two sample groups of ballots for each county to count by hand. These samples can be all ballots cast at selected Election Day precincts or early voting sites, or all the absentee ballots cast in a county. The State Board then informs the counties of their sample groups of ballots and which contest on the ballots to count.
For primaries and elections that include a presidential contest, the contest audited is always the presidential contest. In other elections, the contest audited is the top contest on the ballot. Bipartisan teams of trained volunteers count the selected ballots by hand. Then, they compare the hand-counted results with the results counted by the voting machines and note any differences. Minor differences between the hand count and the machine count are not unusual for the following reasons:
The machine did not count a selection made by a check mark or X or where the bubble or box was lightly shaded by the voter.
The voter did not fill in the write-in oval but wrote a candidate's name on the line.
Human error during the hand count.
(Bold mine)
More info at link
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